BYTNAR - TALKS
EPISODE 013 - APPROVED DOCUMENT A - STRUCTURES - PART 2
This episode is for people who want to know more about Approved Document Part A - Structure.
You should like this episode if you ask yourself questions like:
What does Approved Document A say about preventing disproportionate collapse in buildings?
How do consequence classes (Class 1 to 3) impact building design requirements for robustness?
What lessons were learned from the Ronan Point collapse that influenced current structural regulations?
What are the stability tie requirements for Class 2a and Class 2b buildings?
How is structural robustness tested when removing load-bearing elements in a building?
What factors determine if a building falls into Class 3 for disproportionate collapse risk assessment?
How are fire risks evaluated for structural safety in line with Approved Document A?
Are basement stories exempt from disproportionate collapse requirements, and under what conditions?
How do engineers balance safety and commercial considerations when designing for robustness against disproportionate collapse?
This is Bytnar Talks the Engineer Takes on Construction Episode 13 hi I'm Piotr Bytnar each day I help my clients plan and design building projects through Bytnar Limited a Consulting Chartered Structural Engineers practice my biggest passion and the corner stone on which I've built my business is find finding clever solutions for construction projects I am a chartered structural engineer and a bing software developer so you can rest assured that I will strive to talk about the best practices and the use of new technologies in the industry and if you're embarking on a construction project or are involved in planning designing and building the world around us you'll find this podcast [Music] useful approv documents structure part [Music] two hi there and welcome back to the Bitner talks your favorite podcast on all matters of architecture engineering and construction it is Thursday the 18th of August 2024 and I'm here back with you with the 13th episode and 30 information on approved documents it has been yet another busy week and I had a pleasure and opportunity to visit BAE Systems down in Rochester it is great to see how the biggest employer or the second biggest employer if you take the NHS into consideration within our neighborhood is delivering groundbreaking technology to the airspace Maritime and transportation Industries it was an excellent example of how the six sigmas andl principles are being applied in the research and development driven organization not to mention the fact that I could use the simulators and fly some nice Jets including the fighter ones with the top and newest technology on [Music] board last week in episode 12 I talked about the first two parts of requirement a structures I talk about the loading and ground movement and decided to talk about the disproportion collapse separately in this episode I did that due to the fact that the loading and ground movement requirements are straightforward to apply but the aspects of disproportional collapse give some further complexity to the consideration of the structural safety of the building all right so let us have a closer look at the subject so without further Ado let's dive into the disproportionate collapse requirements of the approved document [Music] many good aspects of innovation are serendipitous in nature and many aspects of low and our conscious are of the hindsight following a disaster such is the beginning of this disproportionate collapse requirement which started with a run on point collapse on the 16th of May 1968 killing four people if you don't know what Ron and po collapse is is it is a 22 story residential Tower made of concrete panels assembled on side unfortunately the construction technique was not robust enough and lacking sufficient mechanical connection between the panels which led to a catastrophic consequence of a localized failure a gas explosion due to a leaking gas cooker connection pushed the walls out allowing several stories over to collapse and in turn take the remaining bottom stories with them interestingly enough the lady who fired up the kettle did not die from the force of the explosion and it is being said that the that she even took the cooker with her to the next place apparently she didn't take the kettle as it had a quite a big dent in it and apparently due to this dent a forensic engineering came up with the idea of what sort of pressure could have could have been exerted by that EXP explosion and settled on 34 K per M Square so here you have it a localized accident leading to a large damage that is not proportionate to the cause is what the disproportionate collapse requirement is all about in this episode I will discuss the consideration that the Secretary of State draws our attention to and further expand on the consideration of risk and fire when it comes to building assessments I will go Section by section giving you simple reasons behind the text and my commentary all right so let's get on to [Music] it the requirement A3 which is disproportionate collapse is put in place to give us all round more robust structures taken in consider ation the risk and consequence of their disproportionate collapse as however the Secretary of State gives us his interpretation of the requirement and consideration that should form part of a structural safety consideration in section five of the approved documents called reducing the sensitivity of the building to disproportionate collapse so you see it's not about elimination but it's about reducing the Sens sensitivity as ever with all of our low applications with all our low lws out there we be dealing a lot with reasonable and reducing rather than giving you some concrete advice although obviously Secretary of State tries to to do his best here as we know this is only guidance and guidance and argument should you have a need to protect your specification and build but building officers generally have no other way of knowing different so it is generally considered as a minimum standard yet using it on its own does not mean that design and build complies with the requirement the person who designs the project and specifies all the elements and people who build them then and then people who operate the building need to make their own judgment and need to assure that they know what they're doing okay so what is it all about it is about ensuring the building is robust enough for the consideration class it falls under consequences classes as these are called are simple divisions of building into groups or rather classes for different and more stringent considerations this follows the general philosophy of approved documents starting with the guidance of approved documents and ends up with systematic analysis of the building from first principles in different failure scenarios so what what are the classes what are we talking about when we talk about the consequences classes of of buildings under the consideration of of robustness of disproportionate collapse there are basically four classes identified by by the guidance by the approved document but in fact there are five and the fifth is sary which means outside of the scope of of all of the four classes that are identified within the guidance so the classes start from one and go to three with a split of Class 2 to 2 a and 2B 2 a being the lower risk group and the 2B being the upper risk group and then class three which Structural Engineers like me love like bzel of honey but let us go from lowest class first shall we class one buildings are build buildings that can be built using the non-engineered approach following approved documents if you want to find out what the non-engineered approach is I'd like you to guide you to to the previous episode where I talk a little bit more about A1 and A2 consideration of the approved document then we go to class 2 a which considers buildings that can follow the requirement of class one but need additional horizontal ties of the walls or need to make sure that the floors are held down to the wall this requirement can be near nearly read one to one with the reasons why the run on point collapsed floor was not tied down to the walls and wall did not tie to the floor so when the explosion happened the floor have been lifted releasing the walls from the slot which were then pushed out all led to the to the catastrophic collapse class 2B goes a step further and requires horizontal and vertical ties between loadbearing elements slap to beam or wall beam to column or wall and and vice versa so all all the structural elements carrying load should be tied tied somehow alternatively to the previous approaches the building may be checked for stability and and the extent of damage by interrupting building system load path through the removal of supporting elements so you can remove like a wall a column or a beam supporting column and see what happens if no more than 15% of the story limited to 100 m squared gets destroyed and the damage does not impact any other story then the then the immediately over and under the building is considered robust by the secretary of state but should the damage extend over the limit the removed load bearing element should be strong enough to take the pressure exerted upon it by explosion of Le leaking gas cooker which is taken as 34 K per M square if we can the element get a nickname and becomes known as key element then we go to class three building in class three needs to be looked into with more care and understanding taking in consideration all probable and reasonable possibilities of the building failure including terrorist attacks and fire so we know what needs to be done but what on Earth are these buildings in section 5.3 the approved document goes on to elaborate on this so for example length of the wall considered for the removal will depend on the material and construction and generally follows the panel story high and two and a quar story wide panels for concrete or internal walls panels and otherwise the panel between lateral supports would be would be sufficient to be taken in consideration for the tributary tributary load path of of that panel to the key element when considering the element for key element consideration the explosion load should be considered vertically and laterally so in both planes explosion Doesn't Really Happen only in one way trying to push walls but it also tries to push ceilings and floors so it should be taken in this this direction also so buildings under consideration are as follows class one buildings houses four stories and smaller isolated buildings meaning with no immediate neighborhood or one half one and a half times the building hide away from buildings that in most cases will not impact more than a single large family if they collapse class 2A buildings are lower risk group houses five story high if impacting only one Family Hotels flats and offices up to four stories three story industrial buildings three story R but with a limit of 2,000 M squar of floor area per story single story education buildings public buildings of Max two stories with a limit of 2,000 square m of floor area per story class 2B buildings with our upper risk group includes accommodation educational office and Retail buildings of up to 15 stories hospitals up to three stories public buildings up to 5,000 m squares of floor area and car Parks up to six stories class three buildings are buildings which exceed the limits of pre of previous classes and include Grand stands over 5,000 Spectators and special designation buildings dealing with hazardous substances and processes interestingly basement stories may be excluded from the calculations of stories if they are at the least CL to be construction so they robust enough at the higher class then they can be excluded from the calculation for more complex buildings risk may be evaluated and addressed by following following recommendations of i t Publications as an alternative approach or other Publications referenced by the Secretary of State truth be told you need to understand the possible risks and find the way to either mitigate on the worst case scenario or eliminate it did we think that the World Trade Center Twin Towers could be impacted by Boing 767 no but they did should we design all buildings for airplan impacts I will leave you with I will leave you with this thought similarly with the impact of earthquakes the approved document does not require typical buildings of class one to 2B to be assessed in this way but certainly class free buildings or unusual buildings should take this into account in reality though if you are in the earthquake prone area you will likely do your assessment for any building that you design and provide minimum time to show some ductility and failure the bottom line here is the relationship of the risk to the to the severity of failure to the to its consequence in relation to harm to people commercial commercial risk is another kind of deliciousness but here we talk about people safety safety in and around the building and that leads us nicely to to the risk so what is risk in this proportionate collapse as and it is as in any other scenario it is the combination of likelihood and severity of Any Given event in Structural Engineering we will identify the risk that decide to Eric the hell out of it what does ering the hell out of it means it means either eliminate reduce in form and control the risk or if we cannot readily identify the issue we will take an approach of limitation of consequences of localized failures such as seen in the approaches with classes a to2 b any any respectful engineer will look at the design from from their perspective and from the perspective of possible risk but that will be highly influenced by by their wisdom meaning well we knowed experience and knowledge not the years of of experience because that's irrelevant in some circumstances it may not be prudent to just follow the expectation of the approved document and the risk evaluation may be better approach ESP especially when we modify existing buildings so knowing what the what the risk is and what we're talking about here when we approach the robust Nest one of the big risks On Any Given projects and aspects that sort of fall outside or are not mentioned within the A3 requirements is fire the requirement of the approved document is with Locker circumstances and mainly focuses on load path during accidental situation one such accidental situation can be an event of fire that albate not acting momentarily but usually impacting the entire compartment or a floor and in this way possibly many load buring elements the general approach to deal with fire in buildings is to isolate or reduce temperature influence of the given fire scenario on given loadbearing element by the provision of protection or oversizing that element it would be unreasonable to build all type of buildings and then burn them down to the ground to provide accurate guidance so we rely on Elemental fairness testing and some typical topology buildings full scale down to destruction fire testing it is however impossible to account for all circumstan ens es and for all qualities of execution to ass certain and make big op optimizations the way the industry generally pushes to the other interesting fact is that materials are often tested to standards that may fail to recognize all aspects of given material like the propagation of Heatwave within the timber that may lead to a fail failure P the test finish or simply to reflect the intensity and duration of the particular fire naturally the temperature change of structural elements can lead to localized values at the intersections with other elements especially where the elements are restrained fire risk should be looked at from the perspective of a fire engineer who will analyze possible scenarios and Structural Engineers who will qualify the risk to the structure that such scenario brings about making sure the building remains robust under the fire condition may prove the most difficult design aspect of them [Music] all so here you have it approved document a requirement A3 disproportionate collapse to sum up shortly the requirement for disproportionate collapse aims to ensure buildings are robust enough to with stand of various scenarios considering the risk its consequences of failure and accounting for a certain level of uncertainty the secretary of state provides guidance through approved documents outlining different consequences classes classes 1 2 three with increasing stringency as the number goes up class one buildings include small structures built to approve documents class 2A requires additional ties for stability addressing risk identifying during forensic investigation of the runand point collapse class 2B Necessities horizontal and vertical ties between load buring elements alternatively buildings can be tested by removing supporting elements if damage remains localized the structure is deemed robust class free buildings undergo comprehensive risk assessments including factors like terrorist attacks and F fire specific criteria determine which building fall in each class considering Factor like height occupancy and construction type basement stories may be exempt from calculations if built to a higher standard for complex structures alternative risk evaluation methods may be employed balancing safety and Commercial considerations fire safety is a crucial aspect focusing on protecting loadbearing elements from temperature influence through ins ation or oversizing however testing standards may not fully capture real world scenarios for Elemental fire approach Engineers analyze fire risks in line with the fire Engineers evaluation of possible fire scenarios and their intensity to ensure structural Integrity during and post the fire balancing risk safety and Commercial interests but focusing on protecting people's safety in and around buildings is Paramount and the reason for a robust structural [Music] design thank you for staying with me all the way till now I hope the added commentary and simple reasons behind the documents paragraphs made your understanding of the matter that little bit better if you have any questions reach out to me on LinkedIn or send me an email I'm more than happy to help you out you can book a non obligatory consultation on our website www.bar.ca.gov and execute their dream homes or Investments if your building is falling apart we can also help investigating the reasons behind it and providing you with an appropriate strategy design and specifications for the repair next week I'll start talking about the requirement B fire thank you again for listening please voice up your opinions I'm waiting for you on LinkedIn and I want to hear from you Toodloo!
Piotr Bytnar BEng (Hons) MSc CEng MIStructE
Chartered Structural Engineer who deals with the Architecture of buildings. His Master's Studies led him to an in-depth understanding of risk and contract arrangements in construction as well as specialist knowledge in soil mechanics.
He and his team help homeowners and property developers to design and deliver construction projects reducing waste in time and the cost. He believes that the construction project is an iterative process that can be well managed and it is best managed if all the aspects of the project definition and management are dealt with in-house or coordinated by one organisation. His team works to all stages of RIBA and ISTRUCTE stages of work and enables contractors to deliver projects on-site providing risk evaluations, methodologies for execution of works and temporary works designs.
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